Heat-sensitive copying-paper



Oct. 29, 1963 R. OWEN 3,108,896

HEAT-SENSITIVE COPYING-PAPER Filed Oct. 26, 1959 I lO-SOURCE orRADIATION l4 REPRODUCED IMAGE H fi & HEAT-SENSITIVE SHEET GRAPHICORIGINAL l3 RADIATION- ABSORPTIVE IMAGE AREAS GRAPHIC ORIGINALHEAT-SENSITIVE LAYER PROTECTIVE LAYER HEAT'SENSITIVE LAYER CARRIER INVEN TOR.

RICH ARD OWE N B 5% dam 6M {#7 ATTORNEYS United States Patent "ice3,108,896 HEAT-SENSITIVE *C OPYlNG-PAPER Richard Gwen, Brooklyn Center,Mind, assignor to Minnesota Mining and Manufacturing Company, St. Paul,Minn., a corporation of Delaware Filed Get. 26, 195i, Ser. No. 843,753 8Claims. (Cl. 117-368) This application is a continuation-in-part of mycopending application Serial No. 594,540, filed June 28, 1956, nowPatent No. 2,910,377.

This invention is concerned with improvements in heat-sensitivecopying-paper useful in preparing copies of printed matter byprocedures, such as those described in Miller Patent No. 2,740,896,involving placing a printed or other graphic original in heat-conductiveassociation with the heat-sensitive copying-paper and then brieflyexposing the graphic original to intense radiant energy. The resultingelevated-temperature pattern produces in the copying-paper a visibledirect copy of the graphic original. The present invention provides astable heat-sensitive copying-paper based on a new principle ofoperation and capable of providing duplicate copies having improvedappearance as well as other advantages.

For convenience in describing the novel copying-paper and itsapplication to the copying of documents, the product and procedure areillustrated in the accompanying drawing, in which:

FIGURE 1 schematically illustrates in cross-section one method ofcopying a graphic original;

PZGURE 2 similarly illustrates an alternative method; and

FIGURE 3 illustrates in cross-section a preferred form or"heat-sensitive copying-paper.

A commercially available thermo-copying machinewidely employed forcopying ofiice records on heat-sensitive copying-paper includes as thesource of radiant energy a high-intensity infrared lamp such as a GET-3" lamp having a linear coiled filament supported within a reflectorwhich focuses the radiation in a narrow beam across the sheet as thelatter is moved past the lamp assembly. Such a lamp draws 1350 watts at280 volts to provide a color temperature of about 2800 K. Irradiationand copying of a conventional letter-size sheet requires about l-6seconds. A non-fading copy is directly produced by such irradiation andwithout any subsequent processing such as developing, fixing, washing,treatment with fumes or vapors, or any other treatment.

in FIGURE 1, radiant energy from source 10 is directed throughheat-sensitive copying-paper 11 to printed original 12. Energy isselectively absorbed in printed areas 13 and released in the form ofheat energy, causing the occurrence of a visible change in correspondingareas 14 of the heat-sensitive layer 15 of sheet 11. The procedure isknown as front-printing.

In FIUURE 2 the radiant energy from source impinges directly on theprinted surface of the graphic original 22, and the resulting release ofheat energy causes visible change in the heat-sensitive layer on support26 at areas 24 corresponding to the printed and radiationabsorptiveareas 2 3 of the original. The procedure has been termed back-printing.

The copying-sheet 11 of FIGURE 1 consists of a heatsensitive layer 15 ona carrier 16, which may be a thin paper. The sheet must transmitsufficient of the radiant energy to provide the required release of heatat the printed areas 13 but is preferably sufliciently visibly opaque toprovide high contrast in the copy.

Still greater accuracy of copy is obtained by inverting thecopying-paper 11 so that the heat-sensitive layer 15 is more closelyassociated with the printed surface of the graphic original 12. In thiscase a visibly transparent ates-nae Patented Get. 29, 1%63 carrier 16permits viewing of the copy areas 14 through the carrier and in the samedirection as the original.

The front-printing process of FIGURE 1 is applicable to a wide varietyof originals and to radiation-transmissive copy-paper, whereasback-printing is most effective with originals printed on relativelythin heat-transmissive paper and the copy-paper may be fully opaque tothe radiation employed.

FIGURE 3 illustrates a further variation in' heat-sensitivecopyingpapers inwhich the heat-sensitive layer 35 is applied to acarrier web 36 and is covered with a protective layer 37. Either or bothof web 36 and layer 37 may be visibly transparent, but in a preferredconstruction for front-printing operations the web 36 is transparentwhile the thin protective layer 37 is visibly opaque and provides highvisual contrast for the visibly changed areas of the heat-sensitivelayer.

The actual temperatures developed in such heat-sensitive papers by thesevarious techniques have not been directly measured. However it has beenobserved that papers which change visibly when momentarily pressedagainst a metal test bar heated to about l20 C., or at most to about 150C., become similarly altered under the irradiation techniques justdescribed. On the other hand, papers which do not change on briefpressure contact with the test bar at temperatures much greater thanabout 150 C. are found to be ineffective as heat-sensitivecopying-papers when tested in copying-machines as describedhereinbefore. Since heating to such high temperatures, particularly whenprolonged or frequently repeated, is likely to cause degradation ordeterioration of the printed page forming the original of which a copyis desired, copy-sheets are ordinarily required to be visiblyheat-sensitive at temperatures below about 150 C. and preferably attemperatures below about C.

Heat-sensitive copying papers suitable for the copying of printed andother graphic originals by methods just described have previously beendeveloped, and such products are described in Miller et al. Patents Nos.2,663,654- 2,663,657, in Taylor et a1. Patent No. 2,668,126, and inClark et al. Patent No. 2,710,263. The sheet materials of the presentinvention operate through a different mechanism than do these prior artmaterials and provide a number of advantages thereover, as will bepointed out hereinafter in connection with illustrative but non-limitingexamples.

Like the earlier heat-sensitive copying-papers, those of the presentinvention are suitable for making direct, high contrast, clear detail,permanent copies of typewritten, printed, and other graphicsubject-matter. The copypaper does not adhere to nor deface the graphicoriginal or the thermoprinting apparatus. It is stable at normal roomand storage temperatures, and in particular may be stored in the lightwithout visible change either before or after heat-copying. The presentinvention additionally provides for the utilization of new classes ofvisibly heatsensitive compositions comprising an intimate mixture ofcomponents including an organornetallic oxidizing agent and a cyclicorganic reducing agent as hereinafter identified, which whensufficiently heated, as in the thermocopying process described, undergoan oxidation-reduction type reaction resulting in the formation of oneor more visibly distinct reaction products. These components arenormally employed in conjunction with a water-resistant film-formingbinder, the combination being in the form of either a self-supportingthin film or a thin coating or coatings on a suitable paper or othercarrier web. The reactants are present in amounts sufiicient to provideadequate visible change on heating, and the binder maintains thereactants in the required intimate but physically distinct associationand in position on the paper backing. A similar effect may be obtainedby retaining the reactants within a paper or other fibrous carrier inthe substantial absence of resinous binder. Additional components, bothinert and chemically reactive, may be included to improve the appearanceor handling properties of the sheet, or to provide a more intense ordifierently colored heat-image, or for other purposes.

As organometallic oxidizing agents I employ normally solid salts oforganic acid anions and readily reducible polyvalent base metal cationshaving a standard reduction potential greater than one-tenth volt.Stearic, behenic, oleic, lauric, hydroxystearic, acetic, phthalic,terephthalic, butyric, m-nitrobenzoic, salicylic, phenyl-acetic,pyromellitic, p-phenylbenzoic, undecylenic, camphoric, furoic andacetamidobenzoic acids are all useful, but best results in terms ofresistance to moisture and fingerprinting are attained with thewater-insoluble salts of the higher molecular weight acids, and inparticular the higher fatty acids such as stearic or behenic acid. Themetallic ion is selected from those polyvalent base metal ions having astandard reduction potential greater than one-tenth volt, viz. theferric, ceric, cupric, mercuric, stannic, bismuthic, thallic andpalladic ions. Of these, the first four named, and more particularly theferric and ceric cations, provide relatively easily prepared,economical, non-poisonous, light-colored and easily reducible oxidizingagents and are greatly preferred in the practice of the invention.

Reducing agents which have been found useful in conjunction with some orall of the foregoing base metal salts include the following illustrativecompounds: 4,4- dimethylamino triphenylmethyl cyanide (malachite greenleuco cyanide); pyrogallol; 4-azeloyl-bis-pyrogallol; 4- stearoylpyrogallol; galloacetophenone; di-tertiary-butyl pyrogallol; gallic acidanilide; methyl gallate; ethyl gallate; normaland iso-propyl gallate;butyl gallate; dodecyl gallate; gallic acid; ammonium gallate; ethylprotocatechuate; cetyl protocatechuate; 2,5-dihydroxy benzoic acid;l-hydroxy-Z-naphthoic acid; Z-hydroxy, 3-naphthoic acid; phloroglucinol;catechol; 2,3-naphthalene diol; 4-lauroyl catechol; sodium gallate;protocatechualdehyde; 4-methyl esculetin; 3,4-dihydroxy benzoic acid;2,3-dihydroxy benzoic acid; hydroquinone; 4,4-dihydroxy biphenyl;3,4-dihydroxyphenylacetic acid; 4(3,4'-dihydroxyphenylazo) benzoic acid;2,2-metl1ylene-bis-3,4,5-trihydroxybenzoic acid; orthoand para-phenylenediamine; 4,4',4"-diethylamino triphenylmethane; m-, and p-aminobenzoicacids; alpha and beta naphthols; and 4-methoxy,l-hydroxydihydronaphthalene. More broadly, there are encompassed cyclicor preferably aromatic organic reducing agents having an active hydrogenatom attached to an oxygen, nitrogen or carbon atom which is directlyattached to an atom of the cyclic or aromatic ring. These reducingagents may be further characterized as being readily visibly oxidizable,a property which is conveniently determined as follows. A small amountof a dilute solution of the organic compound in a water-misciblesolvent, e.g. one ml. of a 5% solution of the compound in acetone, ismixed with an equal amount, e.g. one ml. of a 5% solution, of ammoniumpersulfate in water, and the mixture is momentarily heated on a steambath. A distinct color change is obtained. In general, the color changeis the same as is observed on heating a copy-sheet prepared with thesame reducing agent, although in some instances the color may be maskedor otherwise modified by other components of the copy-sheet.

The organometallic oxidizing agent and organic reducing agent to beemployed in a specific copy-sheet are further selected as capable ofundergoing an oxidationreduction reaction when the sheet is heated inthe thermographie copying process. In all cases the oxidation-reductionreaction causing the visible change in the copysheet will involve achange in the valence of the metallicion, which change in valence may bedetermined anayltically. However any visible effect produced by suchvalence change is ordinarily negligible, at least as compared ferred.When plasticizers for the resinous binder are found to be desirable,phosphates and phthalates, having low water absorption properties, aresuperior to glycols and their esters. Waxy materials may be incorporatedfor added moisture-resistance. Zinc sulfide, titanium dioxide,diatomaceous earth, and numerous other pigments and fillers are usefulin conjunction with the protective surface coating. Dyestuffs may beadded. Metal powders and carbon black may be used in substantialproportions in back-printing papers, and have been found useful in verysmall proportions in the surface coatings of front-printing papers, e.g.to provide somewhat higher sheet temperatures. Pigments and otherparticulate materials such as glass cullet or sphericles may also beadded to the heatsensitive coating for special purposes where desired.

The following specific examples further illustrate the invention.

Example 1 ous solution of three moles of sodium stearate with an aqueoussolution ofone mole of ferric sulfate, followed by washing and drying.Six parts by weight of the insoluble solid product is dispersed in asolution of one part of polystyrene resin in 43 parts of ethyl acetateby grinding in a ball mill for 8-l6 hours to provide a uniform and veryfine dispersion. To a portion of the ferric stearate dispersion is addedan equal molal quantity of 4- methoxy-1-hydroxydihydronaphthalene, withthorough mixing. The mixture is coated on map overlay tracing paper andthe sheet is dried in a current of air at room temperature. The driedcoating weighs approximately one-half gram per square foot of area. Thesheet is light bull" in color, and is converted to a blue color atheated areas in the thermographic reproduction process and on momentarycontact with a metal test bar at C.

Extraction with ethyl alcohol of the blue, completely heat-convertedareas removes the blue image-forming material without removing eitherthe residual iron salt or the polystyrene binder. The solution testsnegative for iron.

A small amount of 4-methoxy-l-hydroxy-dihydronaphthalene is dissolved inacetone, and a portion is added to an aqueous solution of ammoniumper-sulfate in the same amount and at the same concentration. Moderatebrief warming of the mixture on a steam bath produces a distinct bluecoloration in the test solution. a

The 4-methoxy-1-hydroxy-dihydronaphthalene may b separately mixed withbinder solution and applied to the carrier web, the ferric stearatesolution being applied subsequently over the dried first coating, toprovide a copy-sheet which is somewhat less economical to manufacturebut is capable of providing useful heat-copies. The two mixtures mayalternatively be separately coated and dried on separate thin papers,the coated surfaces pressed firmly together, and the resulting compositeemployed in making a copy by the processes here described followed byseparation of the two coated surfaces. Copy thus formed is notsusceptible to modification by further heating.

The copy-sheet of Example 1 is preferably further provided with a thinopacifying and protective contrast coating of titanium dioxide or othersuitable pigment in a film-forming binder, the heat-copy then beingvisible through the transparent paper carrier and against thecontrasting white background.

Example 2 Ceric behenate is prepared as follows: Sodium behenatesolution is first prepared by heating together for one hour at 70 C. amixture of 25 grams of behenic acid, a solution of 3 grams of sodiumhydroxide in 400 ml. of 95% ethyl alcohol, and 400 ml. of water.Separately, 6.2 grams of ceric sulfate is dissolved in water, and thetwo solutions are mixed together with vigorous agitation. The pH of themixture is adjusted to 4.5 with nitric acid. The precipitated soap isrecovered on a filter, washed free of sulfate ion, and dried at 55 C. Itis pale yellow in color. Analysis shows a cerium content equivalent toapproximately one-half of that required for complete reaction with thebehenic acid.

The cerium behenate-behenic acid mixture is intimately dispersed inresinous binder solution by ball milling, a slightly larger molal amountof 4-methoxy-l-hydrox dihydronaphthalene is added, and the mixtureisapplied to a transparent carrier and dried, all as described inconnection with Example 1. The resulting colorless heatsensitivecopy-sheet yields blue image-forming areas in the thermographicreproduction process and on momentary contact with the heated metal testbar.

Cenic stearate is equally as eifective as the eerie behenate-behenicacid mixture. The free behenic acid or other long-chain normally solidfatty acid is not essential but is found to improve the stability of thecopy-sheet under high humidity storage conditions.

Example 3 Mercuric behenate is combined with methyl gallate byprocedures as already described to provide an initially colorless stablecoating which produces a brownish green image when the coated sheet isemployed as a heat-sensitive copyapaper for thermographic reproduction.The metal ion is reduced to a lower valence state without visiblechange. The methyl gallate is oxidized to a visibly different compound.A similar color change occurs when methyl gallate in acetone is added toammonium persulfate in water with gentle heating; a brownish yellowcolor is immediately produced.

Example 4 To a solution of 24 grams of eupric nitrate trihydrate in 500ml. of water is added 14 grams of salicylic acid and 350 ml. of methylalcohol, forming a clear solution. To this is next added sufficientsodiurn hydroxide solution to precipitate the cupric salicylate. Thelight green precipitate is recovered on a filter, washed and dried. Itmelts at 286 C. A 2.5 gram portion is dispersed in a solution of 2.5grams of ethyl cellulose in 50 grams of acetone by vigorous shaking. Tengrams of the dispersion is next mixed with an equal weight of a solutionin acetone of 4% methyl gallate and ethyl cellulose, and the mixture iscoated on map overlay tracing paper at a coating thickness of 3 mils,and dried at room temperature. The resulting pale green colored sheet isconverted to dark brown on momentary contact with a metal test bar at150 C. and is useful as a heat-sensitive copypaper.

Example 6 Bismuth stearate is prepared by the rapid addition of hotsodium stearate solution in 1:1 ethanolzwater mixture to a 4% aqueoussolution of bismuth sodium tartrate. The white precipitate is cooled,filtered, and dried under vacuum for 24 hours at 60 C. Ten grams of thesoap is intimately dispersed in a solution of 3 grams of 6 polystyreneresin in grams of methylethylketone by prolonged milling in, the ballmill. To ten grams of the resulting suspension is next added 0.5 gram ofmalachite green leueo cyanide, and the resulting mixture is applied topaper and dried. The resulting sheet is pale green in color, rapidlyconverting to dark green-blue at C. on the test bar, and producingcopies having good contrast when tested in the thermographicreproduction process.

Malachite green leuco'cyanide rapidly forms a dark green product onwarming in solution with ammonium persulfate.

Example 7 Malachite green leuco cyanide and ferric stearate, suitablymixed and coated, provide a heat-sensitive. copysheet which convertsfrom bull to blue-green in thermographic copying and on momentarycontact with the metal test bar at 100 C.

What is claimed is as follows:

1. A heat-sensitive copy-sheet suitable for the thermographicreproduction of differentially radiation-absorptive graphic originals asherein described, comprising a thin flexible sheet material including avisibly heat-sensitive layer comprising (a) a normally solid salt of anorganic acid anion and a readily reducible polyvalent non-ferrous basemetal cation having a standard reduction potential greater thanone-tenth volt, and (b) a cyclic organic reducing agent for said metalions, having an active hydrogen atom attached to an atom which isselected from the class consisting of oxygen, nitrogen and carbon atomsand is directly attached to an atom of the cyclic ring, said reducingagent being further characterized as providing a distinct color changewhen added in dilute solution in water-miscible organic solvent to anequal concentration or" ammonium persulfate in water with momentary mildheating, said components'(a) and (b) being maintained in said layer inphysically distinct relationship and being so selected and maintained asto be visibly chemically inter-reactive in an oxidation-reductionvalence-change reaction on brief contact of said copy-sheet with a metaltest bar at a conversion temperature within the approximate range of90150 C.

2. A heat-sensitive copy-sheet suitable for the thermographicreproduction of differentially radiation-absorptive graphic originals asherein described, comprising a thin carrier web and a heat-sensitivecoating thereon including (a) a film-forming binder, (b) awater-insoluble normally solid salt of an organic acid anion and areadily reducible polyvalent non-ferrous base metal cation having aStandard reduction potential greater than one-tenth volt, and (c) anaromatic organic reducing agent for said metallic ions, having an activehydrogen atom attached to an atom which is selected from the classconsisting of oxygen, nitrogen and carbon atoms and is directly attachedto an atom of the aromatic ring, said reducing agent being furthercharacterized as providing a distinct color change when added in 5%solution in water-miscible organic solvent to an equal small volume of5% solution of ammonium persulfate in water with momentary mild heating,said components (b) and (0) being maintained in said coating inphysically distinct relationship and being so selected and maintained asto be visibly chemically inter-reactive in an oxidation-reductionvalence-change reaction on brief contact of said copysheet with a metaltest bar at a conversion temperature Within the approximate range of90150 C.

3. A heat-sensitive unitary copy-sheet suitable for the preparation ofright-reading high-contrast reproductions of differentiallyradiation-absorptive graphic originals by thermographic front-printingprocedures, comprising in order a thin transparent carrier web, aheat-sensitive coating, and a ivisibly opaque protective coating, saidheat-sensitive coating being capable on momentary contact of saidcopy-paper with a metal test bar at a conversion temperature within theapproximate range of 90- 150 C. of being converted to a visibly distinctform having high contrast with said opaque coating, said heatsensitivecoating comprising (a) a film-forming binder, (b) a water-insolublenormally solid salt of a higher fatty acid anion and a readily reduciblepolyvalent nonferrous base metal cation having a standard reductionpotential greater than one-tenth volt, and (c) an aromatic organicreducing agent for said metallic ions, having an active hydrogen atomattached to an atom which is selected from the class consisting ofoxygen, nitrogen and carbon atoms and is directly attached to an atom ofthe aromatic ring, said reducing agent being further characterized asproviding a distinct color change when added in 5% solution inwater-miscible organic solvent to an equal small volume of 5% solutionof ammonium persul-fate in water with momentary mild heating, saidcomponents (b) and (0) being maintained in said coating in physicallydistinct relationship and being so selected and maintained as to bevisibly chemically inter-reactive in an oxidation-reductionvalence-change reaction on brief contact of said copy-sheet with a metaltest bar at a conversion temperature Within the approximate range of90-150 C.

4. A heat-sensitive copy-sheet suitable for the thermographicreproduction of differentially radiation-absorptive graphic originals asherein described, comprising a thin flexible sheet material including avisibly, heat-sensitive layer comprising (a) a normally solidwater-insolubie ceric salt of a higher fatty acid, and (b) an aromaticorganic reducing agent having an active hydrogen atom attached to anatom Which is selected from the class consisting of oxygen, nitrogen andcarbon atoms and is directly attached to an atom of the aromatic ring,said reducing agent being further characterized as providing a distinctcolor change when added in dilute solution in Water-miscible organicsolvent to an equal concentration of ammonium persulfate in water withmomentary mild heating, said components (a) and (b) being maintained insaid layer in physically distinct relationship and being so selected andmaintained as to be visibly chemiically inter-reactive in anoxidation-reduction reaction on brief contact of said copy-sheet with ametal test bar at a conversion temperature within the approximate rangeof 90-l50 C.

5. A heat-sensitive copy-sheet suitable for the thermographicreproduction of differentially radiation-absorptive graphic originals asherein described, comprising a thin flexible sheet material including avisibly heat-sensitive layer comprising (a) a water-insoluble normallysolid salt of a high molecular weight organic acid anion and a readilyreducible polyvalen-t non-ferrous base metal cation having a standardreduction potential greater than onetenth volt, and (b) a solid aromatichydroxy reducing agent capable of undergoing a distinct color changewhen added in dilute solution in Water-miscible organic solvent to anequal concentration of ammonium persulfate in Water with momentary mildheating, said components (a) and (11) being maintained in said layer inphysically 7 ponents (a) and ([1) being maintained in said layer inphysically distinct relationship and in condition for visible chemicalinter-reaction in an oxidation-reduction valencech-ange reaction onbrief contact of said copy-sheet with a metal :test bar at a conversiontemperature Within the approximate range of 90l50 C.

7. The copy-sheet of claim 6 in which the ce-ric salt is cericbe'henate.

8. The copy-sheet of claim 6 in which the eerie salt is ceric stea-rate.

References Cited in the file of this patent UNITED STATES PATENTS1,844,199 Bicknell et 'al. Feb. 9, 1932 2,504,593 Schoen Apr. 18, 19502,663,654 Miller et al Dec. 22, 1953 2,663,656 Miller et al. Dec. 22,1953 2,663,657 Miller Dec. 22, 1953 2,910,377 Owen Oct. 27, 1959

1. A HEAT-SENSITIVE COPY-SHEET SUITABLE FOR THE THERMOGRAPHICREPRODUCTION OF DIFFERENTIALLY RADIATION-ABSORPTIVE GRAPHIC ORIGINALS ASHEREIN DESCRIBED, COMPRISING A THIN FLEXIBLE SHEET MATERIAL INCLUDING AVISIBLY HEAT-SENSITIVE LAYER COMPRISING (A) A NORMALLY SOLID SALT OF ANORGANIC ACID ANION AND A REDILY REDUCIBLE POLYVALENT NON-FERROUS BASEMETAL CATION HAVING A STANDARD REDUCTION POTENTIAL GREATER THANONE-TENTH VOLT, AND (B) A CYCLIC ORGANIC REDUCING AGENT FOR SAID METALIONS, HAVING AN ACTIVE HYDROGEN ATOM ATTACHED TO AN ATOM WHICH ISSELECTED FROM THE CLASS CONSISTING OF OXYGEN, NITROGEN AND CARBON ATOMSAND IS DIRECTLY ATTACHED TO AN ATOM OF THE CYCLIC RING, SAID REDUCINGAGENT BEING FURTHER CHARACTERIZED AS PROVIDING A DISTINCT COLOR CHANGEWHEN ADDED IN DILUTE SOLUTION IN WATER-MISCIBLE ORGANIC SOLVENT TO ANEQUAL CONCENTRATION OF AMMONIUM PERSULFATE IN WATER WITH MOMENTARY MILDHEATING, SAID COMPONENTS (A) AND (B) BEING MAINTAINED IN SAID LAYER INPHYSICALLY DISTINCT RELATIONSHIP AND BEING SO SELECTED AND MAINTAINED ASTO BE VISIBLY CHEMICALLY INTER-REACTIVE IN AN OXIDATIN-REDUCTIONVALENCE-CHANGE REACTION ON BRIEF CONTACT OF SAID COPY-SHEET WITH A METALTEST BAR AT A CONVERSION TEMEPRATURE WITHIN THE APPROXIMATE RANGE OF90-150*C.